Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.96   8.578%   $267.0584   $267.06   $267.05   $267.10  
  Purchase #2 $135.50   12.259%   $152.1109   $152.11   $152.10   $152.10  
  Purchase #3 $79.64   6.153%   $84.5402   $84.54   $84.55   $84.50  
  Purchase #4 $223.88   6.795%   $239.0926   $239.09   $239.10   $239.10  
  Purchase #5 $42.58   4.276%   $44.4007   $44.40   $44.40   $44.40  
  Purchase #6 $180.43   5.866%   $191.014   $191.01   $191.00   $191.00  
  Purchase #7 $104.34   9.127%   $113.8631   $113.86   $113.85   $113.90  
  7 purchase totals = $1,012.33       $1,092.0799   $1,092.07   $1,092.05   $1,092.10